Preparation,Properties And Sensing Applications Of Layered Semiconductor Nanomaterials

Layered semiconductor nanomaterials usually refer to the layered materials which have thickness of nanoscale at least in one dimension,such as graphene,carbon nitride nanosheets(g-C3N4),molybdenum disulfide(MoS2),tungsten disulfide(WS2),and so on.These nanomaterials have several obvious advantages of large specific surface area,good fluorescence activity,high stability,good biological compatibility,and environmental friendliness.Therefore,layered semiconductor nanomaterials are considered to be very promising materials for chemosensing and biosensing.In this dissertation,the study was focused on the preparation,properties and sensing applications of graphene quantum dots(GQDs),graphite-like carbon nitride(g-C3N4 NSs),and molybdenum disulfide(MoS2),on the basis of which several chemical and biological sensors have been developed for the detection of H2O2,glucose,folic acid(FA)and Cr2O72-ions.During the study,several new electric and optical properties have been found for these layered semiconductor nanomaterials,which is of great significance both for the development of sensing methods with high sensitivity,high selectivity,low-cost,and environmental benignity,and for expanding the applications the the layered semiconductor nanomaterials.The dissertation is composed of six chapters:Chapter 1:Firstly,the principle and advances of electrochemiluminescence(ECL),the main sensing technology used in this work,was respectively introduced and reviewed.Then the basic concepts,properties of layered semiconductor nanomaterials,the advances of the study and applications of layered semiconductor nanomaterials in sensing were introduced and reviewed,and the development prospects of layered semiconductor nanomaterials was mentioned.Finally,the purpose,content and significance of this dissertation were introduced.Chapter 2:We investigated nanostructures in humic substances(HS)and found that abundant natural graphene quantum dots(GQDs)were contained in HS,and thus proposed a green,low-cost,and efficient way to obtain large amount of GQDs.Four soluble HS including one fulvic acids and 3 different humic acids were investigated in details.Our study showed that all of the HS contained a lot of GQDs with thickness ranging from 0.4 nm to 2.0 nm.These GQDs exhibited unique optical and electric properties,including UV-Vis absorption,fluorescence and electrochemiluminescence.These findings are helpful for better understanding of HS,and the unique optical properties of the natural GQDs make HS have promising applications in bioimaging,biomedicine,and sensing.Chapter 3:We systematically studied the electrochemiluminescent(ECL)behaviors and properties of GQDs/SO32-system,and its ECL interactions with H2O2,and on the basis,a chemosensor and a biosensor were constructed.Our investigation results showed that GQDs had stronger ECL activity than carbon quantum dots due to having a higher density of surface state.Further studies showed that H2O2 could quench the ECL of GQDs/SO32-by the redox reaction between H2O2 and SO32-.Finally novel H2O2 and glucose sensors were constructed base on the GQDs/SO32-ECL sensing system.Chapter 4:We used reduced graphene oxdie(rGO)to hybridize carbon nitride nanosheets(g-C3N4NSs)to solve the issue of over oxidation of pure g-C3N4NSs that led to the passivation of working electrode and then instability of ECL signal,and constructed a very stable solid-state ECL sensing interface based on g-C3N4 NSs-rGO,based on which the ECL reactions between g-C3N4 NSs and folic acid(FA)were investigated.Our experimental results showed that FA can strongly quenched the ECL of g-C3N4 NSs/S2O82-co-reactant system even at very low concentration of FA,and the ECL quenching contained a dynamic quenching mechanism.At last,a sensitive,stable and selective ECL sensor was constructed base on the interactions between folic acid(FA)and g-C3N4 NSs,with a wide linear response range from 0.1 nmol/L to 90 nmol/L,and an excellent detection limit of 62 pmol/L.Chapter 5:We developed a new type of biosensing materials and meoth based on using g-C3N4 as an ECL internal reference and immobilized luminol as ECL sensing luminophore.A new type of solid-state ECL sensing membrane was fabricated by modifying g-C3N4 loaded with luminol on the glassy carbon electrode.The use of g-C3N4 NSs not only can fix luminol on the electrode with its film-forming-ability,but also can acts as an internal reference to eliminate the error caused by electrode passivation and other factors.Based on the new ECL sensing materials and strategy,we have developed sensitive and accurate ECL sensors with an ECL internal reference for the detections of H2O2 and glucose.For H2O2,the linear response range was 0.05μmol/L to 50 μmol/L and the detection limit was 23 nmol/L,whereas for glucose,the linear response range was 0.1 μmol/L to 200 μmol/L,and the detection limit was 20 nmol/L.Chapter 6:Preparation,investigation on electric and optical properties,and related sensing applications were carried out for MoS2 nanosheets(MoS2 NSs).The nanosheets were prepared from bulk MoS2 powder with a lithium ion intercalation method,and purified by high speed centrifugation.The nanosheets have heights between 2 um and 7 um,and lateral sizes less than 100 nm.MoS2 NSs had very weak ECL activity but exhibited good fluorescence property.The fluorescence of MoS2 NSs could be selectively quenched by Cr2O72-,on the basis of which a fluoresence sensor for Cr(VI)has been constructed with a linear response range from 2 μmol/L to 2000 μmol/L,and a detection limit of 1.8 μmol/L.